The episode, which premiered on Saturday, also features CG dinosaurs and recreations of Victorian London. Read on to find out how these were created.

Step 2

Milk designed and created the T- Rex in the opening sequence.

The brief included ensuring the T-Rex was the same height as Big Ben in order to create a dramatic opening moment for this episode as the camera pans round to reveal that the dinosaur is in central London.

Step 3

Image: It's a dinosaur next to the Houses of Parliament, what else could it be except Doctor Who? (or an ill-advised remake of One of Our Dinosaurs is Missing)

Step 4

The focus of Milk’s work was the sinister and mysterious Half-Face Man, the principal villain who appears throughout the episode.

Half-Face man appeared throughout the episode necessitating a high shot count with face replacement required for the majority of his appearances," revealed Milk's Will Cohen. "The high quality required for the cinema release of this episode had to be achieved on a TV budget, which added to the challenge."

Cohen continued: "The tracking of the face replacement required extreme precision by Milk’s match move team lead by Amy Felce. To assist with this critical element, we took a 360 degree photo scan of actor Peter Ferdinando's head and subsequently created a highly accurate 3D model. This mesh then helped our tracking team to lock-in reference points to his natural head shape."

"The actor also had prosthetic make-up masking the missing side of his head. This helped twofold, as it gave us more tracking information and for very wide shots it allowed the shot to be graded down into shadow."

Step 5

"The character’s costume included a top hat to which Milk added tracking markers, as well as to the bridge of his nose and the centre of his forehead.

"This allowed us to accurately matchmove all the rotations and translations of the head," said Will Cohen. "Once we had tracked the movements of the head we were able to line up the accurate 3D model to the live action head. In addition, a full-scale physical model was also built for use on set both for a small number of shots and as lighting reference for us."

"The asset build for the internal workings of the Half-Face man’s face involved creating CG cogs and pistons for which we built a fully automated rigging system. Each shot was then animated to add movement and detail to the mechanism as well as animate and line up the CG eye with the actor’s natural eye-line and movement."

Step 6

It was essential to light Half-Face Man’s CG face absolutely accurately – matching it perfectly to the on set lighting environment in order to ensure the complete believability and consistency of the character throughout the episode.

"In order to achieve this we photo-scanned all the different environments he appeared in," revealed Will Cohen. "This provided our lighting and rendering team, led by Darren Byford, with a virtual set in which to work. Combined with the reference from the practical dummy and high-resolution photo reference we were able to gather a wealth of information to work with."

Ahead of the compositing process, Milk's roto prep team had the monumental task of cleaning up all the tracking markers, removing the prosthetic make up, creating a hollow head, and finally building up the missing bits of his hat and collar. This had to be done on every single shot.

The compositing team then worked in each environment to finalise the look and accuracy of Half-Face man’s CG head.

Step 7

Milk also created a Victorian London cityscape for Doctor Who: Deep Breath.

It included CG builds of the Houses of Parliament, Big Ben and St Pauls as well as wide fly-over views of the Thames as the episode reaches its climax.